A standard cassegrainian concentration optics comprises two reflectors, a primary reflector and a secondary reflector, which are coaxially aligned. The primary reflector captures and reflects incoming radiation to the generally smaller secondary reflector. The secondary reflector in turn reflects the radiation toward the focus of the concentration optics associated with a solar receiver. The primary and secondary reflectors may have different shapes, e.g. the primary reflector may be parabolic and the secondary reflector may be hyperbolic.
The solar receiver may be based on direct absorption of the heat of solar radiation by a working medium, e.g. water, or on a conversion of the solar radiation into another form of energy, e.g. as in photovoltaic cells, in which case the receiver is located with its entrance adjacent to or at the focus of the concentration optics. Alternatively, the receiver may be composed of a means for transmitting the concentrated radiation to a location spaced from the focal point, e.g. for use of solar energy in illumination systems.
Lewis M. Fraas describes in his “PATH TO AFFORDABLE SOLAR ELECTRIC POWER”, LX Crystals Inc., 2004, the use of two different receivers with cassegrainian concentration optics, in which the secondary reflector is in the form of a beam splitter, which reflects concentrated solar radiation in the visible part of the solar spectrum towards fiber optic light guide for piping the radiation to an indoor illumination system, and transmits concentrated solar radiation in the IR part of the solar spectrum towards an array of photovoltaic cells located behind the secondary reflector, for converting the radiation to electricity.
The efficiency of a cassegrainian solar concentrator is highly dependent on the quality of the reflectors' reflecting surfaces. Reflectors exposed to the environment for extended periods, tend to lose their reflection abilities due to, for example, dust or sand erosion, oxidation or corrosion. U.S. Pat. Nos. 4,166,917 and 4,491,683, both describe sealed solar collectors.